Method of preparing technically pure gamma-hexachlorcyclohexane in a cyclic process



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METHOD OF PREPARING TECHNICALLY PURE y-HEXfirElHLORCYCLOHEXANE IN ACYCLIC PROC Paulus Jacobus Petrus Samwel, Weesp, Netherlands, as-

signor, by mesne assignments, to North American Philips Company, Inc.,New York, N .Y., a corporation of Delaware It is known that theinsecticide hexachlorcyclohexane as produced in the additivechlorination of benzene consists of a mixture of a plurality of isomers(a, 8,' ,6,e),'

of which substantially only the 'y-isomer has an insecticide elfect.

For separating the y-isomer from the other isomers several methods areknown, substantially all of which relate to the difierences insolubility of the isomers in solvents. For most solvents the solubilityof the 6- isomer (which is to be understood to include also the e-isomerand isomers other than the a, 6 and 'y-isomers is many times greaterthan that of the -isomer, whilst the solubility of the latter is manytimes greater than that of the isomers a and 3. Several solvents havebeen suggested for this selective crystallisation, for example loweraliphatic alcohols, benzene, cyclohexane, decahydronaphthalene,chloroform, dichlorethylene. The advantages afforded by the use of loweralcohols, more particularly methanol, have become particularly manifest.

Several methods have been suggested for obtaining 'y-isomer of maximumpurity in the crystallisation of 7-is01'ne1 from an oversaturatedsolution which also contains other isomers.

Thus, it would be possible to separate the 'y-isomer by evaporating analcoholic extract of crude hexachlorcyclohexane (in which the alcohol isan aliphatic alcohol containing at most carbon atoms) up to about 40% ofits initial volume and to crystallize the -isomer from the concentratedsolution by means of static crystallisation. It is to be noted that inthe extraction of crude hexachlorcyclohexane by the above-mentionedmethod, a separation of the yand B-isomers from the ocand [3- isomers isobtained, since the latter two isomers dissolve in the said alcoholsmuch less readily than the two firstmentioned isomers.

In another method use is made of the good solubility of the fi-isomer byworking crude hexa to form a paste with the air of methyl alcohol,mixing this paste with an amount of cold methanol and subsequentlypressing out the whole. The main mass which remains containssubstantially all 00-, [iand 'y-isomers, whereas the press juicecontains the e-isomers and small amounts of the -isomer.

In a similar method an extraction is carried out with aqueous methanol.The method may be carried out as a cyclic process and for this purposethe filtrates obtained are used for the extraction of new amounts ofcrude hexachlorcyclohexane.

According to the recognition underlying a further method, this /6separation which precedes the crystallisation of the 'y-isomer would benecessary for carrying out a selective 'y-crystallisation, since thefi-isomer would adversely aifect the crystallisation of the -isomer.According to the said method, crude hexachlorcyclohexane is completelydissolved in a lower aliphatic alcohol i-" temperature comprised between40 and 100 C.,

Patented Sept. 27, 1960 whereupon the isomers a, ,B and 'y are allowedto crystallize by cooling and the mother liquor is removed to use it inthe extraction of a new charge of crude hexachlorcyclohexane. Thecrystallisate consisting of ca, t3 and 'y-isomers is finally againsubjected to an on, ,fi/y-separation.

The retarding influence of the fi-isomer on crystallisation could alsoextend to the ocand B-isomers. In a method based on this recognition,the influence retarding crystallisation is utilised to crystallize the'y-isomer selectively by evaporation from a solution supersaturated withaand B-isomers. This result could be obtained by providing that thesolution supersaturated with a-, ;3 and 'y-isomers contains between 20%by weight and 50% by weight of the fi isomer. This method could also beused in a cyclic process. In order to avoid that an accumulation of thee-isomer may occur in the crystallisa tion liquid, a portion of thefi-isorne r must each time be removed from the liquid flowed back intothe cycle, the quantity thereof, for example, being so chosen that itcontains 'an amount by weight of the S-isomer equal to that which wouldbe introduced into the cycle by extraction of a new portion of crudehexachlorcyclohexane.

Several of the said methods have disadvantages.

Thus, the method having for its purpose to separate the fi-isomer fromthe ot-, [iand' e-isomers by pre-extr-action with methanol or aqueousmethanol has the disadvantage of being not particularly selective, sothat together with the e-isomer an appreciable amount of the y-isomer isextracted from the process.

Said disadvantage is inherent to a lesser extent in the method in whichthe concentration of e-isomer in the crystallisation liquid ismaintained at a value. of from 20% to 50% by weight, but a disadvantageof this method is, apart from what is mentioned hereinafter, that theconcentration of solid substance and hence the viscosity is high.

A cyclic process for manufacturing technically pure 'y-isomer could bedeveloped, which does not exhibit the aforesaid disadvantages.

It is to be noted that in connection with the present invention the termcyclic process is to be understood to mean a process in which asubstance is subjected to liquid extraction, the extract is crystallizedand the mother liquor is used wholly or in part and, if necessary,supplemented with fresh extraction liquid to subject the substance to asecond or subsequent extraction or to subject a new portion thereof tofirst extraction.

The mother'liquor may be supplemented with mother liquors obtained afterrecrystallisation of crystallised *yisomeror with washing liquids of thecrystallisate or with fresh. extraction liquid or, if desired, withmixtures of the aforementioned liquids.

According to the invention, technically pure 6-hexachlorocyclohexane ismanufactured in a cyclic process by subjecting crudehexachlorcyclohexane to a pre-extraction with part of the mother liquorfrom preceding extractions of other portions of crudehexachlorcyclohexane,the amounts of the mother liquor being so chosenthat the amount of e-isomer carried oil. with the preextract is equal tothat present in the crude hexachlorcyclohexane, whereafter the residueof the crude hexachlorcyclohexane thus treated is subjected to a mainextraction with the remainder of the mother liquor from precedingextractions, this extract being evaporated in part and the residuecrystallised after a content of from 5% to 15% of B-isomer has beenreached. 7

In this cyclic process, pre-extr-action is necessary to avoidaccumulation of the e-i'somer in the collected mother liquorsafterrepeated extractions of new portions of hexachlorcycl'ohexane. Thepre-extract contains, in addition to the fi-isomer, the 'y-isomer, butthe amounts of the last-mentioned isomer are small with respect to theamount of 'y-isomer left behind in the residue, since the pre-extractionis carried out with only a small amount of mother liquor.

The mother liquor used for the main extraction may have added to itfresh solvent or any washing liquids of recrystallised amounts of-isomer or mother liquors obtained in such recrystallisations.

The main extraction is preferably carried out with an amount of motherliquor such that the extract is saturated with the 'y-isomer.Extractions with smaller or larger amounts of mother liquor can also becarried out, but they adversely affect the economy of the process. Theproper amount of mother liquor may readily be calculated from thecomposition thereof and the solubility of the 'y-isomer in a motherliqor of known composition. Although several solvents may be used forthe method according to the invention, it is advantageous to utilize forthis purpose lower aliphatic alcohols, for example methanol.

The limit of 5% by weight of 6-isomer has been chosen to form a clearseparation from those technics, according to which the fi-isomer iscrystallized by evaporation from a solution which contains aandfi-isomers, but which does not contain the 'y-isomer, since the latterisomer was removed by means of pre-extraction of the crudehexachlorcyclohexane. The maximum limit of 15% by weight of E-isomer hasbeen chosen to form a clear separation from those technics, according towhich a content of from 20% to 50% of B-isomer is maintained in thecrystallisation liquid.

The invention will now be explained with reference to the examplefollowing hereinafter.

EXAMPLE Mother liquor M 4.4 kgs. of dried and groundhexachlorcyclohexane consisting for 15% (=0.66 kg.) of 'y-isomer, for75% (:33 kg.) of a-l-fl-isomers and for the remaining part (=0.44 kg.)of 8-isomer are stirred for 30 minutes at 20 C. with 1.7 litres ofmother liquor M of a preceding charge and of which the composition isspecified above. The liquid is separated from the solid material bycentrifuging. The liquid has a volume of 1.6 litres containing 0.11 kg.of 'y-isomer, 0.05 kg. of a-l-fl-isomers and 0.44 kg. of 6-isomer. Theamount of 6-isomer introduced with the crude hexa is thus carried ofi.again. The solid material which remained after centrifuging is stirredfor 1 hour at 65 C. with 15.3 litres of the above-mentionedmother-liquor M 5 litres of mother liquor M obtained from therecrystallization of the 'y-isomer, the composition of which is alsospecified above, and 10.2 litres of methanolic washing liquid W,subsequently cooled down to 20 C. and stirred at this temperature forhalf an hour. The liquid was again separated from the solid material bycentrifuging. The product obtained was 31 litres of liquid containing2.15 kgs. of 'y-isomer, 0.75 kg.

which was filtered from the mother liquor.

washed solid material, after drying, weighed 3.3 kg. and consisted,besides for 1.5% of 'y, of a-I-fi-isomers.

43.5 %=13.5 litres were evaporated from the 31 litres of solution. Thesolution concentrated by evaporation was slowly cooled down to roomtemperature (within 18 hours). During this process crude 'y-isomerdeposited The yield was 0.85 kg. of crude 'y-isomer having a content of97.6%. The mother liquor had a composition as indicated hereinbefore byM The crude 'y-isomer was recrystallized from 5 litres of methanol. Themother liquor has the composition as indicated hereinbefore for themother liquor M One obtained 0.5 kg. of lindane having a purity of99.7%. The yield of lindane, calculated on the introduced amount of'y-isomer (0.66 kg), was 76%.

The contentof the difierent isomers was determined by polarographicmeans.

What is claimed is:

1. A cyclic process for the production of technically pure'y-hexachlorocyclohexane by extraction of crude hexachlorocyclohexane,containing the 'y, 6 and other isomers with a lower aliphatic alcohol,in which process mother liquors of preceding extractions arereintroduced in said cyclic process, the undissolved aand B-isomers areremoved, the resultant extract is concentrated by evaporation and the'y-isomer is crystallized out of said concentrated extract by thecooling of said extract and part of the y-isomer is withdrawn from thecyclic process, comprising the steps: extracting a fresh portion ofcrude hexachlorocyclohexane with a relatively small portion of motherliquor of a preceding cyclic process giving a solid pre-extractcontaining about the same amount of 5- isomer as said portion of crudehexachlorocyclohexane, withdrawing said solid pre-extract from thecyclic process, extracting said solid pre-extract with the remainingpart of said mother liquor employed in said pre-extraction, a secondmother liquor of a previous extraction of the crudehexachlorocyclohexane in a previous cyclic process, wash liquidsobtained from crystallizations of the 'yisomer in previous cyclicprocesses and a sufficient quantity of a lower aliphatic alcohol tobring the volume of the liquid employed in said extraction to thedesired level thereby producing a main extract, evaporating part of thealcohol from the main-extract until the concentration of the 'y-isomerin said main extract lies between about 5 and 15% to the desired level,cooling said evaporated extract to room temperature therebycrystallizing out the 'y-isomer and producing a mother liquor, part ofsaid mother liquor being used for the pre-extraction of a fresh portionof crude hexachlorocyclohexane and the remaining part of said motherliquor being used for the main extraction of pre-extractedhexachlorocyclohexane.

2. A cyclic process for the production of technically pure'y-hexachlorocyclohexane by extraction of crude hexachlorocyclohexane,containing the "y, 8 and other isomers with methanol, in which processmother liquors of preceding extractions are reintroduced in said cyclicprocess, the undissolved ocand fi-isomers are removed, the resultantextract is concentrated by evaporation and the isomer is crystallizedout of said concentrated extract by the cooling of said extract and partof the 'y-isomer is withdrawn from the cyclic process, comprising thesteps: extracting a fresh portion of crude hexachlorocyclohexane with arelatively small portion of mother liquor of a preceding cyclic processgiving a solid pre-extract containing about the same amount of B-isomeras said portion of crude hexachlorocyclohexane, withdrawing said solidpre-extract from the cyclic process, extracting said solid pre-extractwith the remaining part of said mother liquor employed in saidpre-extraction, a second mother liquor of a previous extraction of thecrude hexachlorocyclohexane in a previous cyclic process, wash liquidsobtained from crystallizations of the 'y-isomer in previouscyclic'processes and a suflicient quantity of methanol 5 6 to bring thevolume of the liquid employed in said excrude hexaehlorocyclohexane andthe remaining part of traction to the desired level thereby producing amain said mother liquor being used for the main extraction extract,evaporating part of the methanol from the of pre-extractedhexachlorocyclohexane.

main-extract until the concentration of the -isomer in said main extractlies between about 5 and 15% to the 5 desired level, cooling saidevaporated extract to room References Clted the file of this Patenttemperature thereby crystallizing out the 'y-isomer and UNITED STATESPATENTS producing a mother liquor, part of said mother liquor being usedfor the pre-extraction of a fresh portion of 2,57 65 Bender et a1. Nov.6, 1951

1. A CYCLIC PROCESS FOR THE PRODUCTION OF TECHNICALLY PURE$-HEXACHLOROCYCLOHEXANE BY EXTRACTION OF CRUDE HEXACHLOROCYCLOHEXANE,CONTAINING THE $, $ AND OTHER ISOMERS WITH A LOWER ALIPHATIC ALCOHOL, INWHICH PROCESS MOTHER LIQUORS OF PRECEDING EXTRACTIONS ARE REINTRODUCEDIN SAID CYCLIC PROCESS, THE UNDISSOLVED A- AND B-ISOMERS ARE REMOVED,THE RESULTANT EXTRACT IS CONCENTRATED BY EVAPORATION AND THE $-ISOMER ISCRYSTALLIZED OUT OF SAID CONCENTRATED EXTRACT BY THE COOLING OF SAIDEXTRACT AND PART OF THE $-ISOMER IS WITHDRAWN FROM THE CYCLIC PROCESS,COMPRISING THE STEPS: EXTRACTING A FRESH PORTION OF CRUDEHEXACHLOROCYCLOHEXANE WITH A RELATIVELY SMALL PORTION OF MOTHER LIQUOROF A PRECEDING CYLIC PROCESS GIVING A SOLID PRE-EXTRACT CONTAINING ABOUTTHE SAME AMOUNT OF $ ISOMER AS SAID PORTION OF CRUDEHEXACHLOROCYCLOHEXANE, WITHDRAWING SAID SOLID PRE-EXTRACT FROM THECYCLIC PROCESS, EXTRACTING SAID SOLID PRE-EXTRACT WITH THE REMAININGPART OF SAID MOTHER LIQUOR-EMPLOYED IN SAID PRE-EXTRACTION, A SECONDMOTHER LIQUOR OF A PREVIOUS EXTRACTION OF THE CRUDEHEXACHLOROCYCLOHEXANE IN A PREVIOUS CYCLIC PROCESS, WASH LIQUIDSOBTAINED FROM CRYSTALLIZATIONS OF THE $ISOMER IN PREVIOUS CYCLICPROCESSES AND A SUFFICIENT QUANTITY OF A LOWER ALIPHATIC ALCOHOL TOBRING THE VOLUME OF THE LIQUID EMPLOYED IN SAID EXTRACTION TO THEDESIRED LEVEL THEREBY PRODUCING A MAIN EXTRACT, EVAPORATING PART OF THEALCOHOL FROM THE MAIN-EXTRACT UNTIL THE CONCENTRATION OF THE $-ISOMER INSAID MAIN EXTRACT LIES BETWEEN ABOUT 5 AND 15% TO THE DESIRED LEVEL,COOLING SAID EVAPORATED EXTRACT TO ROOM TEMPERATURE THEREBYCRYSTALLIZING OUT THE $-SIOMER AND PRODUCING A MOTHER LIQUOR, PART OFSAID MOTHER LIQUOR BEING USED FOR THE PRE-EXTRACTION OF A FRESH PORTIONOF CRUDE HEXACHLOROCYCLOHEXANE AND THE REMAINING PART OF SAID MOTHERLIQUOR BEING USED FOR THE MAIN EXTRACTION OF PRE-EXTRACTEDHEXACHLOROCYCLOHEXANE.